A patent foramen ovale (PFO) as shown in FIG. 1 is a persistent, one-way, usually flap-like opening in the wall between the right atrium 10 and left atrium 12 of the heart. Since left atrial (LA) pressure is normally higher than right atrial (RA) pressure, the flap typically stays closed. Under certain conditions, however, RA pressure can exceed LA pressure, creating the possibility for right to left shunting that can allow blood clots to enter the systemic circulation.
In utero, the foramen ovale serves as a physiologic conduit for right-to-left shunting. After birth, with the establishment of pulmonary circulation, the increased left atrial blood flow and pressure results in functional closure of the foramen ovale. This closure is typically followed by anatomical closure of the two over-lapping layers of tissue, septum primum 14 and septum secundum 16. However, a PFO has been shown to persist in a significant minority of adults.
The presence of a PFO has no therapeutic consequence in otherwise healthy adults. But patients suffering a stroke or TIA in the presence of a PFO and without another cause of ischemic stroke are considered for prophylactic medical therapy to reduce the risk of a recurrent embolic event. These patients can be treated with oral anticoagulants, but such drugs have the potential for adverse side effects such as hemorrhaging, hematoma, and interactions with other drugs. In certain cases, such as when the use of anticoagulation drugs is contraindicated, surgery may be used to suture a PFO closed. Suturing a PFO requires attachment of septum secundum to septum primum with a stitch (continuous or interrupted), which is the common way a surgeon shuts the PFO under direct visualization.
Non-surgical closure of PFOs has become possible with umbrella devices and a variety of other similar mechanical closure designs developed initially for percutaneous closure of atrial septal defects (ASD). These devices allow patients to avoid the potential side effects often associated with anticoagulation therapies.